Spiral Concentric Two Electrode Sensor Fabricated by Direct Writing for Skin Impedance Measurements

Fundamentals, Recent Advances, and Future Challenges in Bioimpedance Devices for Healthcare Applications

“…Apart from the Ag-AgCl electrodes, other types of electrodes have also been used, such as the gold paste electrodes in the form of two concentric spirals presented in [38] to measure sweat on the skin. As an alternative to gel electrodes, capacitive electrodes have also been proposed as a measurement way that avoids direct contact with the user [92].…”

“…In [100] a 16-electrode probe was used to reconstruct the anisotropic impedance spectrum allowing discriminating neurogenic and myopathic diseases. In other cases, however, a spiral structure has been employed in the electrodes to eliminate the anisotropic properties of the skin and measure the impedance independently of the direction in which the sensing device is located [38].…”

“…EDA sensors can be based on Ag/AgCl disc electrodes attached to the palm sides of index and middle fingers, such as the prototype reported in [335], or multilayered sensor disc for use as a dry electrode [336]. The use of spiral geometry for the electrodes has been suggested in [38] to make measurement results independent of skin anisotropy.…”

“…The anisotropic properties of the skin and tissues must be taken into account, since the flow of the electric current inside the human body is modified by the composition and orientation of the cells in the tissues [88,359]. Since the tetrapolar configuration of electrodes, which is commonly used in bioimpedance measurements, is affected by the anisotropic properties of blood vessels, muscle and nerve fibers [98], new electrode configurations and methods must be investigated to mitigate their effects [38] or allow their measurement as a diagnostic parameter of diseases [98,99,360]. Moreover, the anisotropy is of special relevance in EIT and its incorporation to image reconstruction models using tensors of anisotropic conductivity can provide a higher resolution [361].…”

“…Given their characteristics, bioimpedance measurements allow the characterization of biological media and organic tissues, including the human body, but also inorganic media [38]. In this sense, bioimpedance methods have been employed in skin monitoring (diagnosis of diseases and evaluation of a treatment progress) [38], cancerous tissue characterization and detection [31], sleep apnea detection through bioimpedance measurements [39], as a means of precisely controlling the energy delivered to the heart during defibrillation [40], as a predictor of intradialytic hypotension [41], for precise bone cement milling during revision of total hip replacement [42], for longitudinal knee joint health assessment [43,44], for the evaluation of high-resolution temporal information corresponding to pharyngeal swallowing [45], to monitor the ischemia and viability of transplanted organs [46,47], edema determination [48], brain and pulmonary function monitoring [49,50], and even as a method for the noninvasive measurement of glucose level [51].…”